In a widely used disposable electrode in the electromedical art, the contact member of the electrode is constituted by a separate, usually annular metallic member mounted on a flexible plaster-like support, which may either have been provided with an adhesive coating during manufacture, or onto which such an adhesive is supplied immediately prior to the use thereof.
On one hand, such an electrode construction is not very comfortable to the human skin due to the restriction of the engagement between the hard metallic member and the skin to the very small area of a circular arc, this small contact area giving also rise to difficulties in the provision of measuring signals which are sufficiently free of noise and disturbances. On the other hand, the manufacturing costs of such electrodes have appeared to assume such a level that the intended use as disposable electrodes is counteracted by economic considerations. In some cases, reuse of electrodes of this kind has been attempted by cleaning and washing, whereby the cost level will increase due to an increased load of work.
It has been suggested to make a cheaper disposable electrode, which is also more comfortable to the skin, by replacing the metallic contact member by contacting means of a textile material which has been made electrically conductive by carbonization or graphiting, such as disclosed in Danish Pat. No. 122,258. However, practice has shown that such electrodes suffer from severe problems with respect to suppression of noise and offset potentials. Therefore, these electrodes are not suitable for applications, in which more accurate measurements are required. Experiments have shown that the optimum electrical performance is still obtained by using metallic contact members, such as those of the silver/silver-chloride type.
From U.S. Pat. No. 3,151,619 a disposable electromedical electrode is known comprising a supporting member, the part of which intended for directly contacting the skin is constituted by an annular contact surface provided with an adhesive coating and surrounding a dome-shaped central portion, in which the contact member is provided in the form of a metallic electrode coating on the concave underside of this dome-shaped portion which defines a cavity for accommodation of an electrolytic paste.
Due to this construction of the electrode with a dome-shaped central portion which throughout the surface facing the skin carries a metallic electrode coating, a greater contacting surface is obtained, on one hand, so that noise may be efficiently suppressed, and a well defined cavity for the electrolytic paste is provided, on the other hand, whereby this paste or jelly will be prevented to some degree from leaking out of the electrode, which has appeared to be a disadvantage in known electrodes having a flat support which does not allow restricted localization of the paste or jelly.